Is the defender still out of bounds? If so, then I'd say safety since the ball is now dead in the EZ being touched by an out-of-bounds player and the force putting the ball in the EZ was his fumble. If not out of bounds, then (assuming no one pushed him out), illegal participation on the defense. A will accept the penalty rather than take the play (otherwise a TD), with enforcement being the 2 yd line since it was a loose ball play.
It's tricky, though...does stepping out constitute "intentionally"? Some of the case plays for 9.6.1 talk about accidentally stepping out (though in reference to A), implying that inadvertently stepping out isn't the same thing. But the 9.6.2 cases are more in line with the strict definition - if you weren't pushed out, then you stepped on your own and that's intentionally. Not nearly as sure on this 2nd part than the 1st.